In a previous study we investigated the effects of age on the micturition characteristics and bladder function of male Fischer rats ages five to seven, 16 to 18 and 22 to 24 months. The 24 hr. water intake and urine output increases significantly with age; 22 to 24 month rats showed a 39% increase in water intake and a 93% increase in urine output compared to five to seven month rats. The intravesical pressure at micturition is 100% greater in 22 to 24 month and 16 to 18 month rats compared to five to seven month old rats with no age-related change in bladder volume at micturition. In the present study, in vitro bladder capacity did not differ between the three age groups although the average plateau pressure significantly decreased with advancing age. Using the isolated whole bladder model, the contractile response to the autonomic agonists bethanechol, phenylephrine, and isoproterenol did not change significantly with age. Similarly, there were no age-related changes in the response of the bladder to non-autonomic drugs (histamine, oxytocin, serotonin, substance P, and PGF2 alpha) except for PGF2 alpha which produced an age-related increase in the maximum bladder contraction. In summary, while in vivo micturition clearly changes with age, the in vitro contractility of the bladders to autonomic agents did not. Therefore, age related differences in micturition would be related primarily to the changes in neuronal innervation and central control of micturition rather than alterations in the contractility of the bladder. In addition, these studies show the importance of correlating in vivo bladder function (micturition frequency and volume, cystometry and urodynamics) with in vitro contractile and functional studies.